1. Field of the Invention
The present invention relates to a fuel cell including electrolyte electrode assemblies and separators stacked alternately in a stacking direction. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes. Fluid passages extend through the fuel cell in the stacking direction such that fluids including at least one of a coolant and reactant gases flow through the fluid passages.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes two electrodes (anode and cathode), and an electrolyte membrane (electrolyte) interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is interposed between a pair of separators. The membrane electrode assembly and the separators make up a unit cell for generating electricity. In use, a plurality of unit cells are stacked together to form a fuel cell.
In the unit cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the “hydrogen-containing gas”) is supplied to the anode. A gas chiefly containing oxygen or the air (hereinafter also referred to as the “oxygen-containing gas”) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy.
In the fuel cell, it is necessary to detect whether each of the unit cells has the desired power generation performance. Therefore, in general, cell voltage terminals provided at the separators are connected to a voltage detection apparatus for detecting the cell voltage of each unit cell or the cell voltage of each predetermined number of unit cells.
For example, according to the disclosure of Japanese Laid-Open Patent Publication No. 2004-79192, a plurality of cell voltage monitors are attached to a fuel cell. Each of the cell voltage monitors includes one housing fixed to the fuel cell, and one or more terminals supported by the housing. The one or more terminals of each of the cell voltage monitors are arranged in parallel to each other in the housing of the cell voltage monitor, and arranged in a row in the stacking direction of the cells of the fuel cell. The housings for the respective cell voltage monitors are arranged in a zigzag pattern on the side surface of the fuel cell.
An internal manifold type fuel cell is one type of the fuel cell. Reactant gas passages (oxygen-containing gas passages and/or fuel gas passages) extend through the internal manifold type fuel cell in the stacking direction. The reactant gas passages are connected to the inlets and the outlets of reactant gas flow fields (oxygen-containing gas flow field and/or fuel gas flow field).
Therefore, if the conventional technique is applied to the internal manifold type fuel cell, for example, a separator 1 as shown in FIG. 7 is used. At one end of the separator 1 in a direction indicated by an arrow X, an oxygen-containing gas supply passage 2a, a coolant supply passage 3a, and a fuel gas discharge passage 4b are provided, and at the other end of the separator 1 in the direction indicated by the arrow X, a fuel gas supply passage 4a, a coolant discharge passage 3b, and an oxygen-containing gas discharge passage 2b are provided.
Cell terminals 5a, 5b are provided on an end surface 1a at the one end of the separator 1 in the direction indicated by the arrow X. Grooves are formed in resin members of the cell terminals 5a, 5b for exposing metal portions 6a, 6b. Terminals of a cell voltage monitor (not shown) contact the metal portions 6a, 6b. 
However, in the separator 1, in order to provide the cell terminals 5a, 5b, the distance H from the end surface 1a of the separator 1 to the oxygen-containing gas supply passage 2a needs to be relatively large. Thus, the surface area of the electrode 7 cannot be large. In order to achieve the desired electrode surface area, the size of the separator 1 needs to be significantly large in the direction indicated by the arrow X.
Further, in order to efficiently achieve the sufficient surface area in the surface of the separator 1, the distance from the end surface 1a to the end surface of the electrode 7 needs to be reduced. Therefore, the opening area of the oxygen-containing gas supply passage 2a is reduced, and the pressure loss in the oxygen-containing gas supply passage 2a is increased.